If you want Discus which you certainly can with your tank, go and read lots of info about keeping them. Keeping Discus is a bit specialised compared to keeping most other freshwater fish so if Discus is your end goal it makes sense to set everything up with them in mind.

Discus are higher temperature fish, like the German Blue Rams. The somewhat higher temperature required limits what plants you can have as well. If you've been happy keeping a reef I'm sure you'll manage a planted Discus tank esp at that size tank but do read up.

Main problem with kribs if I remember correctly is just that they breed like crazy and get aggressive when breeding.

As for schooling fish, I have penguin tetras and really enjoy them, they are fairly rowdy for a tetra though but do school tightly quite often (also split up and bicker amongst each other when feeling safe).

If I had your tank I'd do a south american themed tank with a group of angelfish, cories on the bottom, a smaller pleco and a shoal of tetras big enough not to get eaten by full grown angelfish. It's a fairly "standard" set up but it's standard for a reason and none of the fish are particularly hard to care for or tricky to deal with.